Coating high viscosity liquids



Sept. 14, 1965 F. D. MILLER ETAL COATING HIGH VISCOSITY LIQUIDS FiledJune 12, 1962 INVENTORS BY MK A/TRTMRNEYS Eomlnw E M3310 2250583 E52 opwuSwn m FRANK 0. MILLER JOHN J WHEELER E953 mm; $6035 23 United StatesPatent 3,206,323 COATING HIGH VlSCOSlTY LIQUIDS Frank D. Miller and JohnJ. Wheeler, Rochester, N.Y., assignors to Eastman Kodak Company,Rochester, N.Y., a corporation of New Jersey Filed June 12, 1962, Ser.No. 201,869 3 Claims. (Cl. 117-34) This invention relates to a methodfor coating fluid compositions, and more particularly to a method forcoating viscous fluids at high speeds.

Previous attempts to coat high viscosity fluids upon nonpermeable websupport-s at high speeds such as at least 200 feet per minute havegenerally been unsatisfactory, primarily because air bubbles areentrapped under the coatings. The formation of these bubbles can besuppressed by the coating technique which involves supplying a ribbon offluid coating from a stationary coating device, contacting the ribbonwith a moving web support and subjecting the side of the ribbon adjacentthe web support to a low-er pressure (pressure differential) than theopposite side of the ribbon, as described in U.S. Patent 2,681,294,issued on June 15, 1954 to Beguin. This coating technique allows goodcoatings at moderate speeds, but as the coating speeds are increased to300 feet per minute and higher, correspondingly higher pressuredifferentials must be maintained to prevent bubble formation. However,the use of high pressure differentials introduces other problems inobtaining good coatings. For example, at high pressure differentials, itis difficult to hold the web support on the coating roll. In addition,it is diflicult to obtain coatings free of longitudinal streaks.Therefore, it appears desirable to provide a method for coating viscousfluids onto web supports at high speeds which overcomes the difficultiesencountered by prior art methods.

One object of our invention is to provide a method of coating viscousfluids onto web supports at high speeds. Another object of our inventionis to provide a method of coating viscous fluids onto web supports athigh speeds without forming air bubbles in the coating. A further objectof our invention is to provide a method of coating viscous fluids ontononpermeable web supports at high speeds without the use of highdifferential pressures. Still another object of our invention is toprovide a method of coating viscous fluids onto nonpermeable websupports at speeds above 200 feet per minute. A further object of ourinvention is to provide a method of coating viscous photographicemulsions onto nonpermeable support-s, such as baryta coated paper orcellulose ester film base, at speeds above 200 feet per minute.

Other objects of our invention will appear herein.

We have found that viscous fluids may be coated onto a web support athigh speeds by the coating method which comprises forming a ribboncontaining a distinct layer of the viscous fluid and a distinct layer ofa low viscosity fluid coating composition, contacting the side of theribbon composed of the layer of low viscosity fluid coating compositionwith a web support having an electrostatic potential different than thatof said ribbon, simultaneously supplying the ribbon and the web supportwhile moving the support across and in contact with the ribbon, andsubjecting that side of the ribbon having the layer of low viscosityfluid coating composition to a lower pressure than the other side of theribbon.

The drawing represents a diagrammatic view illustrating an apparatuswhich may be used to practice the coating method of the invention. Theweb support 1 is passed around a grounded metal roll 2 and under adevice 3 for imparting a charge to web support 1. The web support 1 isthen passed around guide roll 4 and thence around 3,205,323 PatentedSept. 14, 1965 grounded metal coating roll 5, .and past a stationarycoating device 6 having inlet means 7 for a low viscosity liquid coatingcomposition and an inlet means 8 to supply the viscous fluid coatingcomposition. The low viscosity fluid coating 7 and the viscous fluidcoating 8 pass through orifices L and L, respectively, and aresimultaneously coated onto the web support 1 in distinct layerrelationship as indicated at 10 and 11. A vacuum chamber 12 is providedto subject the ribbon of coating fluids to a lower pressure on the sideof the ribbon composed of the layer of low viscosity fluid coatingcomposition than the opposite side of the ribbon, and is provided withan evacuation pipe 13 attached to evacuating means not shown.

The utilization of a flow of ionized air to render a web or other sheetmaterial electrically neutral or'to distribute an electrical charge onthe surface thereof is well known in the art, and apparatus forgenerating such flows of ionizedair are disclosed in US. Patents1,678,869, which was granted to M. Morrison on July 31, 1938, and2,497,604, which was granted to P. Henry et al. on February 14, 1950.

The method of simultaneously applying multiple coatings is described inUS. Patent 2,761,791, issued September'4, 1956, to T. A. Russell.Apparatus for applying simultaneously a plurality of coatings isdescribed in US. Patents 2,761,417, issued September 4, 1956 to T. A.Russell et al., and 2,761,418, issued September 4, 1956 to T. A.Russell.

The method of coating fluids onto a support which involves employing alower pressure on the side of the ribbon of coating composition adjacentto the web support than the pressure on the opposite side of the ribbonis described in U.S. Patent 2,681,294, issued June 15, 1954 to Beguin.

Our invention will be further illustrated by the following exampleswhich demonstrate the necessity for incorporating all the aspects ofapplicants combination to achieve high speed coating of viscous fluids.

Example 1 A high viscosity 30% gelatin solution, having a viscosity of3,000 cps., was coated at 110 F. onto cellulose ester film base at therate of .5 to .18 lb. per square feet using a pressure differential of 4inches of water pressure. The maximum speed of coating which could beachieved without the formation of undesirable bubbles was 213 feet perminute.

Example 2 A gelatin solution having a viscosity of 2,500 cps. was coatedonto cellulose ester film base at the rate of .5 to .18 lb. per 100square feet. A pressure differential of 26 inches of water pressure wasrequired to achieve a good coating at a coating speed of 300 feet perminute. At a coating speed of 500 feet per minute, a pressuredifferential of 49 inches of water pressure failed to prevent theformation of bubbles in the coating.

Example 3 The procedure of Example 1 was followed except that a lowviscosity (15 cps.) gelatin coating was simultaneously coated with theviscous fluid of Example 1 so that the low viscosity coating wasadjacent the film base, in accordance with the method described byRussell US. Patent 2,761,791, at the rate of .04 lb. per 100 squarefeet. The maximum speed which could be achieved without the formation ofbubbles was 280 feet per minute.

Example 4 A high viscosity 30% gelatin solution having a viscosity of3,000 cps., was coated at F. on to cellulose ester film base to whichhad been imparted an electrostatic charge of 950 field volts. Bubbleswere formed in the coating at a coating speed of 213 feet per minute.

Example A high viscosity gelatin solution, having a viscosity of 3,000cps., was simultaneously coated (in accordance with the method describedby Russell U.S. Patent 2,761,791) With a low viscosity (15 cps.) gelatinsolution at 110 F. onto a cellulose ester film base to which had beenimparted an electrostatic charge of 950 volts as measured against agrounded metal roll. The low viscosity gelatin solution was appliedadjacent the film base at the rate of .04 lb. per 100 square feet withthe high viscosity gelatin solution thereover at the rate of .5 to .18lb. per 100 square feet. A pressure differential of 4 inches of waterpressure was maintained in accordance with the method described byBeguin U.S. Patent 2,681,294. No bubbles were formed in coatingsobtained at the coating rate of 500 feet per minute. The coatings werehighly satisfactory in all respects.

The above examples demonstrate that a highly unexpected increased rateof coating high viscosity fluids on a web support is achieved when (1) alow viscosity fluid coating composition is simultaneously coated withthe high viscosity coating composition, applying the layer of lowviscosity fluid coating adjacent the support, by forming a ribboncontaining a layer of the high viscosity fluid and the low viscosityfluid in bridging relationship between a stationary coating device andthe Web support, (2) subjecting that side of the ribbon having the layerof low viscosity composition to a lower pressure than the opposite sideof the ribbon, and (3) maintaining an electrostatic potential differencebetween the ribbon and the web support prior to the point of contactthereof. The examples further show that a drastic limitation in coatingspeed occurs when any one of the three requirements are omitted from theinventive method.

7 Our invention is generally applicable to coating viscous fluids athigh speed onto web supports, particularly nonpermeable web supportssuch as a cellulose ester film base or baryta coated paper. Theinvention is especially well suitedto the coating of fluid gelatinouscoating compositions, such as gelatino-silver-halide photographicemulsions and antih-alation pelloid backings, such as carbon blackdispersed in gelatin. The low viscosity fluid may advantageously be agelatinous fluid coating composition.

Other suitable low viscosity fluid coating compositions may be employed.

The viscosity of the fluids which may be coated in accordance with ourinvention range from 1,000 to 60,000 cps. Especially good results areachieved with fluid coating compositions having a viscosity in the rangeof 2,000 to 4,000 cps.

In some instances, it may be desirable to provide web supports havingvarious coatings over the high viscosity fluid coating. Such coatingsmay be coated simultaneously With the high viscosity coating orsubsequently applied either before or after drying the first highviscosity coating. These coatings may range from low to high viscosity.

The low viscosity coating compositions which are employed in theinvention should have a viscosity of about 5 to cps., with particularlygood results being achieved with coatings of 5 to 20 cps.

The differential pressure which may be employed in carrying out theinvention may be from 1" to 10" of water pressure and preferably isabout 4 inches of water pressure.

While we have found it convenient to obtain the required potentialdiflference between the web support and the coating fluid by theapparatus shown herein, there are many other means of achieving thispotential difference which will be readily apparent to those skilled inthe art.

The important consideration is that there be a different electrostaticpotential between the web support and the coating composition prior tothe point of contact. This total difference in potential should bebetween 800 and 10,000 volts, and preferably is about 950 volts.

The invention has been described in detail With particular reference topreferred embodiments thereof but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

-We claim:

1. The method of coating a fluid having a viscosity of 1,000 to 60,000cps. onto a nonpermeable web support at speeds in excess of about 300ft./min. which comprises:

(1) forming a ribbon containing both a layer of the fluid coating and anouter layer of a fluid coating having a viscosity of 5 to 50 ops,

(2) subjecting that side of the ribbon composed of the layer of fluidhaving a viscosity of 5 to 50 cps. to a lower pressure than the otherside of the ribbon, the diiference in pressure being from about 1 toabout 10 inches of Water pressure,

(3) contacting the side of the ribbon composed of the fluid having aviscosity of 5 to 50 cps. with a nonpermeable web support having anelectrostatic potential different than that of said ribbon, saidelectrostatic potential difierence being from 800 to 10,000 volts, and

(4) simultaneously supplying the ribbon and moving the web supportacross and in contact with the ribbon.

2; The method of claim 1 wherein the fluid coating having a viscosity of1,000 to 60,000 cps. is a gelatino silver halide emulsion, the fluidcoating having a viscosity of 5 to 50 cps. is a gelatinous fluid and theweb support is selected from the group consisting of baryta coated paperand cellulose ester film base.

3. The method of coating a gelatino silver halide emulsion having aviscosity of 2,000 to 4,000 cps. at speeds in excess of about 300ft./-min. onto a web support selected from the group consisting ofbaryta coated paper and cellulose ester film base which comprises:

(1) forming a ribbon containing both a layer of the gelatino silverhalide emulsion and an outer layer of a gelatinous fluid having aviscosity of 5 to 25 cps,

(2) subjecting the side of the ribbon composed of the layer ofgelatinous fluid to a lower pressure than the other side of the ribbon,the difference in pressure being about 4 inches of water pressure,

(3) contacting the side of the ribbon composed of the gelatinous fluidwith said web support, said web support having an electrostaticpotential different than that of said ribbon, said electrostaticpotential difference being about 950 volts, and

(4) simultaneously supplying the ribbon and moving the web supportacross and in contact with the ribbon.

References Cited by the Examiner UNITED STATES PATENTS 1,678,869 7/28Morrison 317-2 2,497,604 2/50 Henry. et a1 28-22 2,681,294 6/54 Beguin117-34 2,761,791 9/56 Russell 117-34 2,952,559 9/60 Nadeau 117-343,082,144 3/63 Haley 117-34 X WILLIAM D. MARTIN, Primary Examiner.MURRAY KATZ, Examiner.

1. THE METHOD OF COATING A FLUID HAVING A VISCOSITY OF 1.000 TO 60.000CPS. ONTO A NONPERMEABLE WEB SUPPORT AT SPEEDS IN EXCESS OF ABOUT 300FT./MIN. WHICH COMPRISES: (1) FORMING A RIBBON CONTAINING BOTH A LAYEROF THE FLUID COATING AND AN OUTER LAYER OF A FLUID COATING HAVING AVISCOSITY OF 5 TO 50 CPS., (2) SUBJECTING THAT SIDE OF THE RIBBONCOMPOSED OF HTE LAYER OF FLUID HAVING A VISCOSITY OF 5 TO 50 CPS. TO ALOWER PRESSURE THAN THE OTHER SIDE OF THE RIBBON, THE DIFFERENCE INPRESSURE BEING FROM 1 TO ABOTU 10 INCHES OF WATER PRESSURE, (3)CONTACTING THE SIDE OF THE RIBBON COMPOSED OF THE FLUID HAVING AVISCOSITY OF 5 TO 50 CPS. WITH A NONPERMEABLE WEB SUPPORT HAVING ANELECTROSTATIC POTENTIAL DIFFERENT THAN THAT OF SAID RIBBON, SAIDELECTROSTATIC POTENTIAL DIFFERENCE BEING FROM 800 TO 10.000 VOLTS, AND(4) SIMULTANEOUSLY SUPPLYING THE RIBBON AND MOVING THE WEB SUPPORTACROSS AND IN CONTACT WITH THE RIBBON.